Telephone system



c. B. FOWLER TELEPHONE SYSTEM Filed Nov. 30. 1923 June 14, 1927.

June 14, 1927. y

C., B. FOWLER TELEPHONE SYSTEM NIE Patented 'June 14, 1927.

.uN1.T:ED-..-sr Arrss RAT ENT Vover121C15;.;j

CLARENCE B. FoWLEra oir-*NEW` YonmNaY.,

inluvr,v 1Neoaroiim'rnn,` or.- NEW Yom; Na y.; A. coRPoRATIoNiQF YOBILTELEPHONE SYSTEM.

Application med Nqvembe; 3o, 1923; serial No.- 677.8%

This invention relates to telephone systems and more particularly toconnecting circuitsl i'or.- use ineXtending connections fromvsub--plurality' of scribers` lines terminating in a connecting terminals.

The object of this invention is toprovide a simplified `and vimprovedcircuity arrange-V ment` tor permitting acalling subscriber to iiash acalling supervisory lamp `as a re call signal, by themere Yact `ofremoving the receiver, from the switchhook.

This ob]ect l1s attained nV accordance with a feature ofthe inventionvbythe provision of means for connecting current to a supervisory signallthrough two parallelpaths 'to actnate the signal in one'manner when acalling subscriber hangs up after complet? ing. a call, andgtorlintermittently diverting. the current around said signal, and throughone of the two parallel paths tooperate the signal in another mannerwhen. the calling,

lDuring the period of conversation between the calling and called`subscribers, the supervisory signal circuit is openedy so that duringthis timethere is no unnecessary current drain from thebattery supply.

In the-drawings, v

Fig. 1 shows a calling'station-A and acalled station J with associatedlinel circuits,` and oneot a plurality ot connecting or linkcircuits@,w'hiclimay be used to interconnect such stations. The stationJ isomer-of, four stations on the lselected'line D, the other ksta#`tions M, W and yIt being shown schematically.

Fig. 2 shows an operators telephonel serandtesting circuit togetherwithparty line t. n u the connecting circuit C.

Each ot' the stations A and .l is shown sionalinoequipment used inconuectionmwith terminatingl at a central oice in a plurality ofanswering jacks and a` multiple jack., Each answeringjack hasausignalingdevice, associated therewith. The lanswering jacks and theirassociated line lamps for ajstaf tion terminate at diierentoperatorsfposi tions. Multiple jacks, only v.one of whichy is 'show-n.in the drawings, operators position.

In the following:detaileddescriptiom,` it, will be first assumed; that4a subscribel at the-@tation A the, calling'subscriber andV 'that asubscriber al; astato W, whe has vcircuits such as C of thevoperatorsposition, operates over a` vcircuit extendingV y:trom

may appear at each i contacts 69 of relay:

a 'telephone equipment similar to the one fullygshownpin station J, is.the called subscriber. Y Y .y

Upon initiating a call, thev subscriber at*y station A removes thereceiver from the switchhook and establishes an obviouscir.-v

cuit for line relay 3,.which relayf thereupon v operates. v Relay 3 Ain"operating, completes a circuit 'extending from' grounded battery,through the filaments ofl lamps 8vr andvv 9,` which lampsare located infront ofdifferent operators atl the central office, any onefof whichoperators may 'answer the call.' ViThe the calling subscribers line.

Upon theinsertion of plug 11 into liack" 12, aistarting relay 20,commonto the link ground, through the winding of cutsotf re-v` layll,sleeve contacts of jack 12"and4 plug 11,

winding and contacts 64 ofimarginalV relay 1st, V'contacts 65 of relay52, conductor 75',

contacts 66 of. relay 31, contacts 670i relay 32,;,windingrv of relay,20, contacts 68 of' ref lay 35, to vgrounded battery over the contacts,

`69`c f1ielay 31. Relays 4 and 1,4 are marginal and do,V ,notV receivesulicientcurrentat this time. to operate. yRelay. 20 lin operating`causes the operationl ofirelay 32,."which in attracting `its inner lefthand armature opens,

atgthe contacts, 67, a, shunt path normally connected around 4thepolarized relays 30 andy 40, connects ground between resistance 19 and',the winding of relay 20.' andati its battery, through; resistance '18,between re-,U lay and. 'resistance V19 vith relay 32 operated,an'dmwithfground `,and grounded outer left hand armature connectsgrounded i battery `connected to resistances vwand-"18, 1'

ment isftormed. j-The closurejot contacts.

edfthrough the contact 68` of 4relay 35 and' A* complet-tA `asdescribe-d, al potentiometer circuit arrange# V 31L to grounded"battery'.`

be had by referring to the patent to Fowler No. 1,517,577,` issued'July28, 1925.

Since the calling line has been assumed to direction. The oath for oieratino` rela i may be traced from ground, through the winding ofcut-ofi' relay 4f, sleeve contacts of jack 12 und plug`11, Winding endcontacts 6/1 ot relay 1, windings et relays 30 and 40, contacts ('ofrelay 32 and thence through one arm of the potentiometer circuit including resistance 18 togrounded battery. It will be noted that currentalsotlows at this time through resistance 18 and resistance 19 (formingthe other arm oi the potentiometer' circuit) to ground, bui` thiscurrenty is incf i fectual.

Relay 3,0 in operating, completes a circuit for relay 31 over a pathextending 'from grounded battery, through the contacts of relay 30, letthand Windingot relay 81, to ground at the right hand contacts otrelay32. Relay 31 thereupon operates and locks over a. path extending fromgrounded battery, over the left hand yalternate contacts l1nd left handWinding ot relay 31, to ground at the right hand contacts of Vrelay 32.

Relay 31 in operating, opens at its contacts 69, the energizing circuitfor relay 20, whereupon relay 2O releases, which in turn 'eleases relay32. Relay 31 in operating,

nalso opens at its-contacts 66, the circuit 'for relay 30, whereuponthis relay releases. In attracting its right hand armature, relay 31connects its right hand winding and. resistance 17 in multiple toconductor 75. This circuit is established before the release off relay32, so that relay 3l remains oiierated after the release of' relay Theconnec tion oi" grounded battery through the right hand winding of relay31 and resistance 17 in parallel, hercinbetore mentioned, in'-creases'the current flow over conductor 175 sullicientlyr to permit theoperation ol'lmargina] relays 4; and 14. Relay 14 in operat ing, locksover a path extending from ground. through the Winding ot' cut-oil"relay L1, sleeve contacts ot jack and plug` l1, Windingr and cont-acts61 ot relay 1.4i 'to groundedbattery. At itsarn'iatinfcs 33 andh 34.relay 1-1-connects grounded battery and K ground to the ,ring and tipconductors of the answering end otlhelinks circuit C through the Windingof supervisory/'relay 13,u'hieh relay'thereupon operates and preventsthe operation of relay 101. At its armature 341,

vrelay 14 also connectsground to the conductor 36 leadinv tov the.osition lashin(T cirn rp cuit. Y

Cut-ott relay 11, operating in the circuit ;`-.bove traced, removes theline relay o trom the calling line, whereupon this relay releases andopens the circult for lamps and V9 which thereupon are extinguished.

the operatofs4 telephone set to the cord cirf cuit.v At its armature1111, relay pregarcs a ci rcuit 'for relay 97 in the operators posi tionequipment and for relay 60. At'its :1rmaturcs 45 and 416, relay connectsthe common ringil'lg leads to the cord circuit, while al" its armature50 it opens the circuit for relay 101.

The opcrators headset being now connected to the cord circuit, theoperator may con- .Verse With the calling subscriber in order (toascertain theI nature ot the desired connection. Upon learning that aparty. on the line D is desired. the operator makes the usual busytestand if the desired line is idle, she inserts the plug 17 ot her cordcircuit into jack l18 corresponding to the dosired line D.

The insertion of plug 4 into jack i8 of the desired line causes relay 52to operate over an abvious sleeve circuit, which includes the Winding ofcut-oli, relay 56. At its right hand armature, relay 52 causes thecalling siiiperyiscry lamp 419 tobe illuii'iinated over an obviouscircuit, and also cornucas battery to the hack Contact of thetripping.relay 84- and to the winding ol,l relay S5. The buttery vat theback Contact oi relay 8/1- cmu-:os current to ilow tln'ough the windingot umrgiv nal relayG() thence over the ifi-uut contact and armature /14et relay 22. ronductor 5l. to ground through the Windinuo'l rcl f 97.Relay 6() docs not receive suilic'umtcurrent at this time to operate.Relay 97. however,

operates to cause the pilot lamp 96 lo glow in an obyious circuit. Atits lefl. hand armature relay 52 opens the original energia ing circuitfor relay 2O at an additional point.

Il. the callingsubscriber :isles` i'or connectionrr'ith party lli/"Q theoperator actuates lteyrlV for un instant t'o cause the desired'pzirl'yto be signaled autoznaticully.

,The actuation oi key W causes relay to operate.' At its contacts 59,relay preparesthe peg count relays, 92 and 93 for operation. It may bestated here tl it thc peg count circuit is employed only when a checkenthe number ot calls handled by an operator is'to be made. Theactua-.tion of key 151 then completes the circuit for these relays andthe registering device 152 will. beroperated Whenever a resigning ortrunk lrey is actuated. y 'Atits contacts "57, relay connects groundtothe conductor 54, thereby shunting' relay 97 and causing the pilotlamp 98v to be extinguished. The current in the circuit including thewinding of marginal relay 60 is now suilicient to cause this relay tooperate. At its contacts 58 relay 75 causes relay 23 to operate todisconnect the operators head-set trom'the cord circuit. Y

`Relay 60 in attracting its armature 24, locks under the control ot bothrelays 84 and '52. ln attracting its armatures 25 and 26, relay 60removes the short circuit Aaround the ring-back tone condensers 88 and89. In

attracting its armature 2-5, relay 60` connects the ground 0n the outerleft hand armature ot relay 7 0 to the tipside ot the calling end of thelink circuit C. At its armature 27, relay 60 completes the energizingcircuit ior theyvinding ot relay 85, Which'wasy initiated by theoperation ot relay 52.

llVith relays and for alspecial code of ringing current is estab! lishedwhich may be traced from the ringing source 13() (Fig.v 2) through theinterrupter 28, conductor 29, contacts 62 o'tf relay 63, Winding ofmarginal relay 84. iront co'ntact and lett hand armature ot' relay ,85,

`outer right hand armatureand back contact of relay 70, iront contactandl armature 26 of relay 60, ring contacts of plug47 and jack 48, andthence through the bells at the subscribers station W, to ground. Thecondensers 88 andr 89 serve to complete `a path back to the callingsubscribers line, thereby enabling the calling subscriber to hear theringing signal.

Should the party R be desired by the calling subscriber, the operatorwould momentarily actuate key R,`v`vhereupon relay 74, operates. At itscontacts 77, relay 74 causes relay 63 to operate in a circuit extendingfrom grounded battery, overy the right hand miniature and front contactof relay 52, back contact andarmature (it tripping relay 84, Winding ofrelay 63, conductor 71, front contact and armature 46 of relay 22,conductor 78 to ground atthe contacts 77 ot relay 74. At its contacts 78, relay 74 causes relay 75 to 'operate causing a closure of the pegcount circuit, the shunting ot relay 97, the extinguishment ot lamp98'aud the operation of relays 60 and 23 as;

hcreinbeore described. y f

Relay 63 in attracting its armature 79, locks up under the control otrelays 84 and 52. At its armature 82, relay 63, prepares a circuit forrelay 83 and at its contact 86 prepares theconnection of lead 87 from.the

ringing current supply to the ring side of the cord circuit.` p

`Atthc proper interval` `battery'from the ringing equipment will beconnected to lead L 90 through the interr1`1pterl91, whereupon 60operated, a circuit Winding'of relay 83, armature 82 and frontcontactfot-relay'l to ground. Relay 83 in attracting its outerarmatureloclis up over `an obvious circuit. At its inner armature,

relay 83'causesa speciallcurre-nt code to be connected tothe ringside ofthecord.` This path-maybe` traced from the ringing current source (Figi2) throughthe inter-4 rupter 94, conductor 87,\front contact and innerarmature ot' relay 83, contacts 86V oit relay 63, Winding of trippingrelay 84, front contact and inner left hand armature of relay 85,conductor 67, outer right hand armature and back contact ofrela-y 70,front* contact and armature 26v ot relay 60, ring contacts ot' plug 47andy jack 48, and the-nce through the bells at the subscribers stationR, to ground.

lit the operator receives a request for party J, she momentarilyactuates the corresponding lrey- J whereupon relay 7 3" oper-- ates tocause relay 7,5 tooperate. The latterV in operating,pe1toi1iis`rtlre'samel functions as in the previous connection. k.At itscontacts 96. relay 73 connects ground to the conductor 9.9, causingrelay 70 to V'op(nate in a circuit extending from grounded battery, overthe righthand armature anditront cone tact ot relay 52, back contact andarmature oi' relay 84, right hand Winding ot relay 70,l front contactand armature`45 of relay 22, conductori'99 to ground at *the contactf96`of relayr73. `f

Relay connects ground to the ring side of the cord circuit C byway ofithe front contact and armature 26 ot' relayGO. At its inner "lett handarmature, relay 70 locks` through its left hand Winding. At its outerrightr hand Winding, relay 70 prepares a circuit for transmittingringingcurrent overthe tip side of the cord and at `its inner right handarmature. establishes an energizing circuit or the right hand Winding ofrelay 85 to grounded battery on the iront contact and right handarmatureof relay` After an interval, slouT `operatingrelay 85 operates and locksto ground on the normal contact 39 of keyv41. At its left handarmature,rc# lay 85. completes the circuit to the tip consri' gli'

70 atits outer lett'hand armature, l

ductor lof the cord circuit initiated by re- Y and jack 48 and thencethrough the bells at Y the subscribers station J to'ground.

To signal the party M, the operator actuates hey M fausing relay 72 tooperate. Relay 72 in operating, causes both relays 73 and 711 tooperate, which in turn cause relay 75 to operate. The .operz'itingcircuits for relays 7 S, 74 and 75 are obvious. Rela-ys 73. 7d Vand 7 5in operating perform the saine Afunctions hereinbeore described inconnection with the actuation of keys J, R, and WT, respectively, and itis believed unnecessary to repeat them.

At theproper interval, battery will beconnectcd to the conductor 00 byWay ot in.- terrupter 01, whereupon rclsy S3 operates to ground on theiront Contact and armature 82 of relay 03. Relay S3 in operating, loc rsunder the control ot relay 03. Y

The circuit ior ringing current may now be traced from the ringingcurrent supply, through interrupter 011, conductor 87, it'ront contactand innerI armature of relay 83, contacts 86 of relay Winding oli'tripping relay 84, front Contact and inner right hand armature of relay85, outer right handv arms ture and `lront contact ot relay 70, frontcontact and armature 25 ot relay 60, tip con-V tacts of plug 47 and jacki8 and thence through the bells at the subscribers station M. to ground.

From the descriptions ot the signaling ot the various parties on a.line, it is apparent that the tip conductor of the cor-d is employed insignaling two of the parties and the ring conductor for the othertivo,and that each party has a special ringing code.

Should the operator neglect to depress the ringing key such as keys M',El", R or 1V for a suiiicient length of time or to a sutilcicnt extent,the ringing pilot lamp 98 Will remain lighted since relay 97 will nothave been shunted down. Upon noting the continued illumination ot lamp98, the open tor Will know that the ringing equipment has not functionedand she Will again actuate the proper key.

ln each ot the preceding ringing'operations, relay in operating, afteran interval. opens the circuit 'tor relay 22, which .in releasingdisconnects the operators telephone setgand the common ringing equip-.xnent troni the cord circuit. It will alsobe noted that altllongllringing` current in each` instance passes through theivinding oit-trip`pine relay 811. this relay is marginal and does not operate until thecalled subscriber` responds to the signal.

When the called party answers the signal, the trippinfr relay Sioperates and opens the locking circuits' ttor relays 00, 70 and 03releasing them, if operated. The oper ation of relay 811 is eiifected inthe follow-A ing manner: lWhen the subscriber such as party J removesthe receiver from the switchhool. the condenser 155 is shortcir]- cuitedby the switchhook contacts, thereby reducing the resistance of thecircuit including relay Si to such an extent as to permit this relay tooperate, it being understood that ground is applied to the tip or ringconductor ot the cord depen-ding on Whether the ringing current isapplied to the ring or tip ot the cord. This ground serves as a returnpath i'or the ringing current when the subscriber removes the receiver.The release oi relay 63 causes relay 83 to restore. Relay 00 inrestoring again shunts the ring back tone condensers 8S and 89, andrenders the tip and ring conductors of the calling end oit' the linkcircuit C continuous. Upon the release oi" the armatures 26 and 9A ofrelay (i0, the calling supervisory relay 100 operates iu an obviouscircuit from battery associated with the repeating coil 15, over theclosed celled subscriber-s line loop. Relay 100 in operating, causeslamp l18 to be extinguished. v

Should the. called subscriber at any time desire to flash. the operator,he may do so by actuating his sivitchhook thereby causin relay 100 tointermittently deenergize an energize, whereupon the lamp 49 flashes insynchronisni with the sivitchhook actuations.

At the termination of the conversation, the called subscriber onrestoring his receiVerIcaus-es.relay 100 to restore Whereupon lamp 4l-9glows steadily serving as a disconnect signal to the operator.

lVhen the calling subscriber hangs up his receiver, answeringsupervisory relay 13 releases, whereupon relay 101 operates in a,circuit. extending from grounded battery, over tho armature 83 andYfront Contact of relay 141, back contact and armature of supervisoryrelay 13, normal make-beforebrealr contacts and Winding of relay 101,back contact and armature 50 ot relay 22 to ground at the Contact 102 otkey 41. Relay 101 in operating locks over a path including its contacts140, back Contact and armature 50 ot relay 22, and contacts 102 of key41. Relay 101 in operating causes the lamp to be lighted over twoparallel paths, one extending from grounded bat-V tery, contacts 140`and 103 of relay 101, rcsistanee element 104i, lilamcnt ot lainp 55 toground on the contacts 105 oi relay 14:, and the other1 troni groundedbattery, armature 33 and 'liront Contact ol? relay 14. hack con-V tactand arnuiture-ot relay 13. front contact and inner right handarmatureo't relay 101, resiftance element 106.l tilainent of lamp 55 toground on the contacts 105 of relay 14,.

The steady glen7 oit' lamp 55 indicates to the` Relay 13 in operatingatthis time, connects sertion of `plug 11 into jack 12, it caused' relay107 (Fig. 2), to operate in acircuit extending from grounded battery,through the Winding of relay 107, conductor 36, and contacts 105 ofrelay 14 to ground. Relay 107 in operatinn', connects the interrupter110, to the winding of relay 108 causing this relay to be intermittentlyoperated.v Relay 108 in operating, intermittently connects groundthrough the Winding of relay 109, over conductor 111to the outer righthand armature of relay 101. Therefore, with ref lay 101 operated andWhen relay lreoperates, thebattery associated-With armature 33 of.relay` 14is` disconnected from the lamp 55 at the back contacts of relay13 and the greater portion4 of the current from thebattery associatedwith the left hand armature of relay 101 passes over the contacts 140and 108ofrelay 101, resistances 104 and 106, inner right hand armatureof relay 101, armature and frontcontact of relay 13, front contact andouterjright hand'armatur'e of relay 101, conductor 111, armature andfront Contact of relay 108 to ground throughtlie Winding of relay 109,when relay 108 risoperated. It is therefore` apparent that each timerelay 108 operates the lain 55v is shuiited and relay 109 operated. `T elamp 55 isaccordingly flashed and relay 109 operatedin synchronisni withthe operations of relay 108. The pilot buzzer 155 is there-y,

by operated to give an audible recall signal.

Upon the receipt of this flashing signal, the operator may remove plug47 from the j ack 48 of the called subscribers linevor may actuate key112. The first operation causes the release of relay 52, Whichopens thelocking circuit for relay 85. Relay 85 in releasing its right handarmature, causes relay 22 to be reopera'ted from battery associated withthe armature 33 of relay 14. Relay 22, in vreoperating'opens at itsarmature 50 and back contact, the locking cir cuit for relay 101, whichthereupon releases and stops the flashing of lamp 55. The actuation ofkey 112 also opens the locking set of relay 101 and bridges the`operators telephone set across the link circuit C.

Lf the plug 47 had already been removed troni Vjack 48, relay 85 Wouldbe releasedso that relay 22 would be reoperated. The locking circuit forrelay 101 would, there fore, be opened at the armature 50 of relay 22,so that the lamp 55 would not be flashed under such a condition. It Willbe noted that under such a condition, when relay 22 releases theoperators head setA is connected across thev cord'and the callingsubscriber may converse with the operatorn'ithout the flashing signal. V

When, at the t tion (assuming plug 47 to bestill. connected with jack48), the .operator removes plug 11 fromv jack 12, relays. 14 and`4-restore, the latter again associatingl the line relay 3 with tlielineA. Relay 14 inret-racting itsarina-f ture 33, opens the circuit forrelay 22`Which releases. `When the operator removes the calling plug 47`from jack 48, relay 52 will termination of the conversa.-

release causing thef lamp 49` toY ,be eXtinv guished and restoring thelink normal. i

On aconnection over a trunk circuit, Wlierein ringing current is notessential to the establishment of a connection the opera ator havingaccess to the link circuitl C, after having inserted the plugs` 11 and47 into the jack` 12 and the jack of the outgoing trunk circuitrespectively, i depresses the', trunk key T. Upon the connection of thelink circuit With the calling line and the outgoing trunk, the samelinkcircuit apparatus Will function as hereinbefore described in connectionwith extending a call from a calling subscriber to a calledv subscriberby circuitV G to Way of the link circuit only. When they ductor 99.Relay operates in thiscircuit and locks through its left hand Windingand` inner left hand contacts to ground, thereby removing its controlfrom relay 22. p

Unless relay 60 is operated, relay 70 per` forms no ringing function. Atits inner right hand armature, relay 70 causes relay 85-to operate in anobvious circuit. Relay 851locks under the control ofkey 41 ,and

opens the circuit for relay 22 which there-` upon releases causing thedisconnectionof the common ringing vand listening equipmentl from thelink circuit. It is therefore appar-f ent that by the actuation of thetrunk key T on a trunk connection, which, correspondsv to the actuationof a ringing key on a subscriber to subscriber 'connect-ion, the ringingequipment associated with the link circuit is prevented from functioningtosend out ring ing current over the connection.-

Should the calling subscriber on initiating' a` call` make a requestforanother party on the saine line, the operator will instruct him Ltoreplace his receiver on the switchhook tor a minute. lVhen theoperatorhears the disconnect click which accompanies the res-` torationof the receiver by the calling subscriber, she removes the plug 11 fromthe answering jack and replaces it with the calling plug 117. Upon theinsertion otl plug Y into Jack 12, relay 52 operates in an obvioussleeve circuit causing relay 22 to operate to the calling party comeback on the connection too soon, that is, before the called party hasanswered the signal, the 4removal oit the receiver by the calling` partywould trip the ringing current as hereinbeore mentioned and would causelamp 19 to light. 'The operator then actuates key 112 to connectherheadset to the link circuit and requests the calling subscriber toreplace his receiver on the switchhook and wait for a short period oftime. The operator then again initiates the ringing of the desiredparty. by actuating the corresponding key.

Having described in detail the arrangement of a connection between asubscriber al station Av and a subscriber at station B, it will now beassumed that the operator at which jack 12 and its associated line lamp8 appears, has answered a call irom the sub-l scriber at station A. andthat an operator at the position at which lamp 9 is located attempts tohandle the call upon noting the illumination of lamp 9. It is to beunderstood that the operator at. such position attempts to handle anincoming` line immediately after the lirstoperater has answered a call,otherwise the lamp 9 would have been extinguished shortly after theinsertion oll plug 11 into jack 12.

The second operator having a cord and associated test and operatorscircuit identical with the one shown in the drawings, inserts plug 11thereof into jack 50.l The sleeve of jack 50 being multipled 'with thatof jack 12, now has a busy potential connected thereto owing to theinsertion of plug 11 of the original cord circuit into jack 12 by thefirst operator. The potential on the sleeve oit' jack 12 has beenprovided from the battery associated with the sleeve oi' the plug of theoriginal cord circuit.

Upon the insertion of plug 11 of the sec- Y ond cord circuit into jack50, an energizing circuit is established for relay 2O over a pathextending from ground through the winding of cut-oill relay l, sleeve ofjack 50 and sleeve 11, winding and contacts 64: of relay 114i, contactsG5 ot' relay 33 contacts 66 of relay 31, contacts 67 of relay 32 windingof relay`20, contacts 68 of relay 35, and contacts 69 of relay '31, togrounded battery. (The apparatus above mentioned is associated with thesecond operators equipment). Another' path for current through thewinding of relay 4 to ground, extends through the sleeves of jack 12 andplug 11, the winding of relay 111, to battery potential, but relay 20 ofthe second operators equipment is of the sensitive type and operates inthe parallel branch to battei-y extending to the second cord. Relay 2()of the second operators equipment in operating, causes the operation ofrelay 32 which closes at its contacts 7.3, the circuit previously tracedtor holding relay 2() operated. Due to thejlfact that a plug at anotheroperators position has been previously inserted into a multiple of thejack 50, the current liowing through the polarized relays 30 andt() isin a direction opposite to that which it was when the line was idle, andis in such a direction as to cause the operation of polarized relay 10only. The reason that the current flows in a reverse direction at thistime is due to the fact that an unbalanced Wheatstone bridge arrangementis formed. A complete discussion of this current reversal at this timemay be had by referring to the above 'identified copending application.l

The operation of polarized relay 40 associated with the second connectedcord circuit, causes the operation of relay 35 and establishes a holdingcircuit "for relay 32 through the right hand windingthereof. Relay 35 inoperating, .releases relay 2O and opens contacts iu the leads from theoperators telephone set extending through the listening key 112 o'l' thesecond connected cord circuit and the listening `keys of the other cordcircuits at the saine operators position. In closing its alternatecontacts, relay 35 connects a source of tone supply 80 to the receiver81 to indicate. to the operator .the busy condition oit the callingline, or

the fact that the call has already been answered by another operator.

The operator noting the tone signal removes the plug 11 of the secondoperators link circuit from jack 50, whereupon relay 110 releases. Relay40 in retracting its armature opens the holding circuit for relay 32which relay-then releases. Relay 35 also releases as a consequence ofthe release of relay 410 and being of the slow-to-release type retractsits armature at an interval after its energizing circuit is' opened atthe contacts of relay 40. Relay 35 in restoring restores the operatorstelephone to normal.

The invention claimed is:

1. In a telephone system, a telephone line, a link circuit, a signal forthe link circuit, a source oi current, means for first connectingcurrent from said source to said signal to actuate said signal when thesubscriber Orsaid line hangs up after completing aV call,

leo

lltl

and means for intermittently shunt'ing said signal to flash said signalwhen the subscriber oi said line recalls.

y 2. In a telephone system, a telephone line, a link circuit, a signal'lor the link circuit,

pleting a call and for intermittently diverting a portion oi saidcurrent around vsaid signal to lflash said signal when a subscriber ofsaid line recalls.

3. In a telephone system, a telephone line, a link circuit, a signal forthe link circuit,

a source ot current, means `for iirst connecting current from saidsource to said signal to actuat-c said signal when the subscriber otsaid line hangs up after completing a call, and means for intermittentlydiverting a portion of said current around said signal to flash saidsignal when the subscriber ot said line recalls.

4. In a telephone system, a telephone line, a link circuit, a source ofcurrent, 'means including a supervisory relay for first connectingcurrent from said source to said signal to actuate said signal when thesubscriber of said line hangs up after completing a call, andinterrupter mechanism for intermittently diverting a portion of saidcurrent from said source around said signal to iash said signal when asubscriber of said line recalls.

5. In a telephone system, a telephone line, a link circuit, a source ofcurrent, means inf cluding a supervisory relay tor first connectingcurrent from said source to said signal to actuate said signal when thesubscriber of said line hangs up after completing a call, andinterrupter mechanism for intermittently diverting a portion of saidcurrent around said signal to flash said signal when a subscriber ofsaid line recalls, said interrupter mechanism being conditioned toroperation when said link circuit is connected to said telephone line.

6. In a telephone system, calling and called subscribers lines, a linkcircuit, a signaling device associated with the link circuit.interrupter mechanism, a sleeve relay lfor the link circuit, anoperators telephone set, means controlled by said sleeve relay forconnecting the operators telephone set to the link circuit, a relayoperated in response to the actuation oit the sleeve relay for preparingthe interrupter mechanism ifor operative relationship with the signalingdevice, a circuit completed for the signaling device when the callingsubscriber hangs up, for steadily actuating said signal device, andcircuit connections for connecting said interrupter mechanism inoperative relationship with said lamp to flash said lamp when thecalling subscriber recalls.

7. In a telephone system, a telephone line, a link circuit connectedthereto, a supervisory relay for the link circuit,a locking relayoperated upon the deenergization of the supervisory relay, a signalingdevice, an operating circuit therefor.including.contacts of saidsupervisory relay and said locking relay vestablished upon thedeenergization of said supervisory relay, interrupter mechanism, andanother .circuit .completed to control the iiashing oi' said signalingdevice upon the subsequent Jenergization oit said supervisory relay,including contacts of said supervisory relay and said second relay.

8. In a telephone system, a telephone line, a link circuit connectedtherewith having an answering and a calling end, a signaling device, asupervisory relay orsaid link circuit controlled over the answering endof said link circuit,` a locking vrelay operated in response to thedeenergization of said supervisory relay to eli'ect a circuit for saidsignaling device, whereby said signaling de- Y vice is actuated, avshunt circuit for said signaling device prepared by the operation ofsaid locking relay and completed by a subsequent.operation of saidsupervisory relay, means for intermittently connecting said shuntcircuit about said signalingdevice to cause said signaling device to beintermittently operated, a key, and means controlled by said key and thecalling end of said link circuit for restoring said locking relay tonormal,thereby stopping `the intermittent operation of said signalingdevice. y

9. In a telephone system, calling and called subscribers lines, aconnecting circuit interconnecting said lines, a supervisory signal, akey, an operators telephone set, means responsive to a disconnection bythe calling subscriber to actuate said supervisory signal in one manner,said means being also responsive to the initiation of a recall signal bythe calling subscriber to actuate said signal in another manner, andmeans responsive to the actuation of .said key for deenergizing saidsignal and bridging said telephone set across said connecting circuit,said means also responsive to the disconnection of said connectingcircuit from said called subscribers line.

l0. In a telephone system, the combination with a telephone line of asubstation switch, a supervisory lamp, a circuit for said klampincluding two parallel branches completed upon the actuation ofsaidsubstation switch, and means responsive to a single subsequentactuation of said substation switch for intermittently connecting one ofsaid parallel branches in shunt of said lamp, causing the same to beVflashed.

11. In a telephone system, a telephone line, a connecting circuitassociated therewith, a. supervisory signal, a circuit for said signalincluding two parallel branches established upon the disconnection bythe subscriber of said line to cause a steady operation of said signal,and means responsive to the initiation in a recall signal by thesubscriber of said line for intermittently connecting said parallelbranches in series relation with each other to cause the flashing ofsaid signal.

12. ln a telephone system, a telephone line, a connecting circuitassociated therewith, a supervisory lamp, means responsive to adisconnection by the subscriber of said line for establishing a circuitincludingl the lilainent of said lamp in series with two parallel branchcircuits, and means responsive to a recall by the subscriber of said'line for intermittently connecting said two branch circuits, in serieswith each other and one thereof in shunt of said lamp.

In Witness whereof, I hereunto subscribe my name this 27th day of Novcinber A. D.,

CLARENCE B. FOWLER.

